1. Technical Field
The present invention relates to a liquid crystal display (LCD) device and a method of fabricating the same, and more particularly, to an LCD device of which a gate wiring is formed of a metal layer of silver (Ag), to improve the uniformity in line width and surface state of the gate line, and a method of fabricating the same.
2. Description of the Background Art
Generally, an LCD device can control the transmittance of light in liquid crystal cells based on a video signal. That is, an image corresponding to the video signal is displayed on an LCD panel which is provided with the liquid crystal cells arranged in a matrix configuration. For this, the LCD device includes an active area which is comprised of the liquid crystal cells arranged in the matrix configuration; and driving circuits which drive the liquid crystal cells of the active area.
FIG. 1 is a plan view of illustrating a related art LCD device. FIG. 2 is a cross section view along A-A′ of FIG. 1.
Referring to FIGS. 1 and 2, the related art LCD device includes upper and lower substrates 10 and 20 facing each other and being bonded to each other, wherein the LCD device is divided into a display region 4 provided with liquid crystal cells; a sealant 2 provided along the circumference of the upper and lower substrates 10 and 20; and a plurality of dots 3 provided in the circumference of the sealant 2, wherein the dots 3 electrically connect the upper and lower substrates 10 and 20 to each other.
Referring to FIG. 2, the display region 4 is provided with the upper substrate 10 including a black matrix 30, a color filter 15, a common electrode 17, and an upper alignment layer 19 which are sequentially formed on a second substrate 11; the lower substrate 20 including a thin film transistor (TFT), a pixel electrode 31, and a lower alignment layer 33 which are sequentially formed on a first substrate 21; and a liquid crystal layer (not shown) which is formed in a space formed between the upper and lower substrates 10 and 20 through the use of spacers 35.
First, the detailed structure of the upper substrate 10 will be explained as follows.
The black matrix 30 is arranged on the second substrate 11, wherein the black matrix 30 of the matrix configuration divides a plurality of cell regions for the color filters 15, to thereby prevent the light from being coherent in the adjacent cell regions.
Then, red (R), green (G) and blue (B) color filters 15 are sequentially formed on the second substrate 11 including the black matrix 30. In order to form each of the color filters 15, a predetermined material layer is coated onto an entire surface of the second substrate 11 including the black matrix 30, and is then patterned, wherein the predetermined material layer absorbs a white light source, and transmits only the light corresponding to a predetermined color (for example, red, green or blue). At this time, the common electrode 17 is formed on the second substrate 11 including the black matrix 30 and the color filter 15, wherein the common electrode 17 is formed of a transparent conductive layer. The common electrode 17 is supplied with a ground electric potential. Then, the upper alignment layer 19 is formed on the upper substrate 10 including the common electrode 17. In this case, the upper alignment layer 19 is formed by coating the common electrode 17 with polyimide.
The detailed structure of the lower substrate 20 will be explained as follows.
First, the thin film transistor (TFT) is formed on the first substrate 21, wherein the thin film transistor (TFT) switches the operation of liquid crystal molecules. The thin film transistor (TFT) is comprised of a gate electrode 25 protruding from a gate line (not shown), and source and drain electrodes 28S and 28D protruding from a data line (not shown). Also, the thin film transistor (TFT) includes a semiconductor layer 26 and 27, and a gate insulation layer 23. In this case, the semiconductor layer 26 and 27 forms a transmission channel between the source and drain electrodes 28S and 28D with a gate voltage applied to the gate electrode 25. Also, the gate insulation layer 23 is positioned between the gate electrode 25 and the semiconductor layer 26 and 27, to thereby insulate the gate electrode 25 from the source and drain electrodes 28S and 28D.
Then, a passivation layer 29 is formed on an entire surface of the substrate including the thin film transistor (TFT). At this time, the passivation layer 29 is provided with a contact hole 29H which exposes the drain electrode 28D. On the substrate including the passivation layer 29, there is the pixel electrode 31 which is formed in the contact hole 29H and is electrically connected with the drain electrode 28D. At this time, the pixel electrode 31 is positioned in the cell region divided by the gate and data lines, wherein the pixel electrode 33 is formed of a transparent conductive material having the high rate of light transmittance. Then, the lower alignment layer 33 is formed on the first substrate 21 including the pixel electrode 31.
The thin film transistor (TFT) selectively supplies a data signal of the data line to the pixel electrode 31 in response to a gate signal of the gate line. According to a voltage difference between the data signal supplied through the thin film transistor (TFT) and a common voltage (Vcom) supplied to the common electrode 17, the liquid crystal molecules are rotated, whereby the light transmittance is controlled based on the rotation degree of the liquid crystal molecules.
After forming the sealant 2 and the dots 3 along the circumstance of the second substrate 11 for the upper substrate 10 or the first substrate 21 for the lower substrate 20, the spherical spacers 35 are scattered on any one of the substrates. After that, the upper and lower substrates 10 and 20 are positioned in opposite to each other, and are bonded to each other. Then, liquid crystal is injected into a space between the two substrates, and is sealed, thereby completing the LCD device.
In the LCD device having the above-explained structure, the gate electrode 25 is generally formed by patterning a metal layer of silver (Ag) in a photolithography method. That is, a layer of silver (Ag) is deposited on the substrate, and is then etched by using an additional photoresist pattern, thereby forming the gate electrode 25.
If using the photolithography method, a photoresist layer is coated in a spin-coating method. In this case, the photoresist layer may be damaged. Also, the photolithography method necessarily requires the exposure and development process of the photoresist layer, and the process of removing the photoresist pattern. In addition, it is necessary to perform a cleaning process between the silver-metal layer deposition process and the photoresist layer patterning process. Accordingly, the exposure process requires a laser exposure device, so that the fabrication cost and time increase.
As explained above, if the gate electrode is silver metal having the great resistivity, the fabrication cost increases due to the expansive layer of silver. Furthermore, if the layer of silver is patterned by the photolithography method, the amount of silver used increases, whereby the fabrication cost increases.
To overcome this problem, instead of the photolithography method, there has been proposed a printing method to form the gate electrode 25 from the metal silver (Ag). That is, the desired portions of the lower substrate are printed with silver, directly, thereby forming the gate electrode 25. The method of forming the gate electrode by the printing method will be explained in detail.
FIGS. 3A and 3B are cross section views of illustrating a method of fabricating an LCD device using a related art printing method.
First, as shown in FIG. 3A, silane molecules are printed onto an insulating substrate 41, whereby a silane pattern 43 is formed selectively. The insulating substrate 41 may be formed of a glass substrate. The silane pattern 43 is arranged at a fixed interval, to thereby expose the predetermined portion for the gate electrode.
Referring to FIG. 3B, a layer of silver (Ag) grows between each of the silan patterns 43 on the insulating substrate by the printing method. Thus, the gate electrode 25 of silver (Ag) is formed on the insulating substrate.
When forming the gate electrode of silver (Ag) by the printing method, the silver grows between each of the silane patterns. In comparison with the photolithography method, the printing method uses a smaller amount of silver. Even though silver used for the gate line has the good resistivity, silver is easily oxidized. Furthermore, if the silane molecules are adsorbed into the silver, the adsorption conditions is troublesome. Thus, it is difficult to obtain uniformity in line width and in the surface state of the gate line.